1. Field of the Invention
The invention relates to an in-vehicle electronic control unit having first and second control circuit portions that are electrically separated and serially communicate monitoring signal and control signal to each other.
2. Description of the Related Art
There have been known in-vehicle electronic control unit including first and second control circuit portions that are electrically separated and serially communicate monitoring signal and control signal to each other, by using of periodic transmission packets for down link communication, periodic report packets for up link communication, and report return packets for up link communication corresponding to reading request packets as down link communication and the like.
The “in-vehicle electronic control unit” disclosed by Patent Document 1: Japanese Patent Laid-Open No. 2003-285702 (paragraph No. 0079, FIG. 2) for example includes a microprocessor connected with a key station serial-parallel converter to form a first control circuit portion, and a combined control circuit portion connected with a sub station serial-parallel converter that is serially connected to the key station serial-parallel converter to form a second control circuit portion. The combined control circuit portion includes first storing means for storing data transmitted from the key station to the sub station, distribution storing means for transferring command data stored in the first storing means to a device memory if the data is a writing/setting command, return packet producing means for producing up link return information to the microprocessor, second storing means for sequentially storing the return information to avoid a traffic jam and reading out the information in a first-in-first-out manner, and return packet organizing means for adding up-to-date information to the packet for return.
As for the return packet, at most 16 pieces of ON/OFF information or digital conversion values for at most 15 analog signals can periodically be returned based by return data 1 and 2. Which data to be returned is determined by an address specified in status data.
Meanwhile, the “analog/digital converter” as disclosed by Patent Document 2: Japanese Patent Laid-Open No. 8-23276 (Abstract, FIG. 1) includes (1) a multiplexer portion responsive to a selection instruction to select one channel among a plurality of channels to which analog signals are input, (2) an analog/digital conversion portion that converts the single analog signal selected by the multiplexer portion into a digital signal, and (3) a control portion that outputs a selection instruction to the multiplexer portion and reads the digital signal produced by the analog/signal conversion portion. Then, (4) the multiplexer portion includes a channel return portion that returns the selected channel to the control portion when the analog/digital conversion portion finishes conversion operation, (5) the control portion includes an abnormality determining portion that determines an abnormality when the channel output by the control portion to the multiplexer portion does not match the channel returned from the channel return portion.
The analog/digital converter includes (6) a multiplexer portion responsive to a selection instruction to select a channel among a plurality of channels to which analog signals are input, (7) an analog/digital conversion portion that converts the single analog signal selected by the multiplexer portion into a digital signal, (8) a control portion that outputs a selection instruction to the multiplexer portion and reads a digital signal produced by the analog/digital conversion portion, and (9) an abnormality determining portion that determines an abnormality when the time necessary for conversion, i.e., the time measured between the output of a conversion start instruction to the analog/digital conversion portion by the control portion and the end of the conversion by the analog/digital conversion portion is not less than predetermined maximum time.
The “in-vehicle electronic control unit” disclosed by Patent Document 1 can alternately and periodically return ON/OFF information as switch signal inputs and digital information as digital conversion values based on analog input signals, but AD conversion must be carried out at frequency sufficiently higher than the cycle of periodic returning in order to obtain digital information as new as possible, which increases the control load on the second control circuit portion.
In the “analog/digital converter” disclosed by Patent Document 2, a channel specifying instruction must be transmitted in advance every time digital information for an analog signal is to be obtained, and the communication control load is high in order to obtain many digital values at high frequency.
In addition, abnormality determination about the AD converter is carried out after the AD converted-digital information is transmitted, and therefore abnormality determination may be late or transmission may be wasted.